Material for joining and product produced therewith

ABSTRACT

The invention relates to an iron-based brazing material comprising a brazing alloy, which alloy comprises: from about 9 wt % to about 30 wt % Cr, from about 5 wt % to about 25 wt % Ni, from about 0 wt % to about 9 wt % Mo, from about 0 wt % to about 5 wt % Mn, from about 0 wt % to about 1 wt % N, from about 6 wt % to about 20 wt % Si. Within the alloy is at least one of the B and the P are present as a melting point lowering supplement to Si, and wherein B is from about 0.1 wt % to about 1.5 wt %, or wherein P is from about 0.1 to about 15 wt % P. The brazing alloy may comprise contaminating elements as at least one of C, O, and S, and optionally the brazing alloy also comprises at least one micro-alloying element as V, Ti, W, Nb, or Ta, and the micro-alloying element is less than 1.5 wt % in the brazing alloy. All values are stated in weight percent, and wherein Si, B and P lower the liquidus temperature, that is the temperature when the brazing material is completely melted.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application of and claims thebenefit of U.S. patent application Ser. No. 10/416,248, having thefiling date of Sep. 19, 2003, and which claims the benefit ofPCT/SE01/02478, having the filing date of Nov. 8, 2001, and which claimsthe benefit of Swedish Patent Application No. 0004118-6, having thefiling date of Nov. 10, 2000, the contents of all of the foregoingapplications being incorporated by reference herein in their entireties.

TECHNICAL FIELD

The present invention relates to an iron based brazing material forjoining objects by brazing. The invention also comprises a brazedproduct produced by brazing together objects of an iron based materialwith an iron based brazing material according to the invention.

BACKGROUND OF INVENTION

Different steels or iron based materials are usually joined by brazingwith Ni- or Cu-brazing materials. In some applications the brazingmaterial may consists of Ag or Co.

Brazing is a process for tightening/joining, at which the temperature isbelow the original solidus temperature of the base material, i.e. theelements that should be joined/tightened.

Brazing materials refer to materials for joining or tightening, whichcompletely or partly melts during the brazing process.

When brazing with Cu one generally uses pure or almost pure Cu. The purecopper brazing material has a well defined melting point, while nickelbrazing materials, depending on the fact that they consists of alloysoften have a melting interval instead.

When joining plates of stainless steel in plate heat exchangers brazingmaterials of copper is often used. Copper is however not suitable forall kinds of applications. The use of brazing material of copper forfood applications is not allowed for example, but it is used fordistrict heating and tap water installations. Heat exchangers joinedtogether with brazing material of nickel are used in many connectionsand are also allowed for a limited number of food applications.

If brazing materials containing nickel alloys are used for joiningobjects of iron or non Ni-based materials, the composition of the brazedjoint differs significantly from the composition of the materials, whichare joined together. This can result in undesired differences inchemical and mechanical properties.

Brazing material wherein the amount of boron is said to be about 2 toabout 6% in order to obtain the desired lowering of the liquidustemperature are known.

SUMMARY OF INVENTION

The brazing material of the invention relates to an iron-based brazingalloy. The brazing alloy comprises from about 9 wt % to about 30 wt % Cr(chromium), from about 5 wt % to about 25 wt % Ni (nickel), from about 0wt % to about 9 wt % Mo (molybdenum), from about 0 wt % to about 5 wt %Mn (manganese), from about 0 wt % to about 1 wt % N (nitrogen), fromabout 6 wt % to about 20 wt % Si (silicon), wherein at least one of B(boron) and P (phosphorous) is present as a melting point loweringsupplement to Si, and wherein B is from about 0.1 wt % to about 1.5 wt%, or wherein P is from about 0.1 wt % to about 15 wt % P. The brazingalloy may comprise contaminating elements such as at least one of C(carbon), O (oxygen), and S (sulphur). The brazing alloy may alsocomprise at least one micro-alloying element such as V (vanadium), Ti(titanium), W (tungsten), Nb (niobium), or Ta (tantalum). Themicro-alloying element may be in an amount less than 1.5 wt % in thebrazing alloy. All values are stated in weight percent, i.e. wt %. Si,B, and P lowers the liquidus temperature, that is the temperature whenthe brazing material is completely melted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the DTA curve for melt no. 2;

FIG. 2 shows the same curve for melt no. 3;

FIG. 3 for melt no. 5

FIG. 4 shows Diagram 1 with the wetting and flow ability tests; and

FIG. 5 shows Diagram 2 with the corrosion tests.

DETAILED DESCRIPTION

The present invention offers possibility to join objects by means ofbrazing by using a brazing material with mainly the same composition asthe base material used for producing the product, at which the brazingmaterial contains additive elements which lower its liquidustemperature. Consequently, the present invention offers a possibility toproduce an apparatus as a plate heat exchanger, which is compatible withfood application requirements by using a brazing material according tothe invention. The brazing material or brazing alloy according to theinvention is iron-based which means that the main element in the alloyis iron (Fe). The brazing material comprises a brazing alloy. Suitablythe brazing material comprises a binder apart from the brazing alloywhen the brazing alloy is in form of a powder, but the brazing alloypowder do not need to be together with a binder, i.e. in someapplications the powder itself could be applied on surfaces to bebrazed. The brazing material could be in form of a paste. In otherapplications could the brazing alloy be a foil.

The invention is mainly characterized in that the brazing materialcomprises a brazing alloy. The brazing alloy may comprise at least 50 wt% Fe according to one alternative according to another alternative maythe alloy be balanced with Fe. The alloy may also comprise, 0-30 wt %Cr, preferably 9-30 wt % Cr, maximum 5 wt % Mn, 0-25 wt % Ni, maximum 9wt % Mo, 0-1 wt % N and 6-20 wt % Si, all stated as weight percent,where addition of Si lowers the liquidus temperature, that is thetemperature at which the brazing material is completely melted.

Apart from Si, the brazing material also may comprise B or P, which actsas a melting point decreasing element supplementing Si. The addition ofB also increases the wettability of the brazing material, which makesthe brazing material to flow when the brazing material is melted. Theboron content in the brazing material may be below about 1.5 wt %. Sinceboron increases the wettability of the brazing alloy then boron need tobe present in an amount of from about 0.1 wt % B to about 1.5 wt % whenB is in combination with Si in the brazing alloy. B may supplement Si asliquidus temperature lowering element and B increases the wettability ofthe brazing alloy. In another embodiment may the iron based brazingmaterial comprise B within a range from about 0.2 wt % to about 1.5 wt%. Instead of adding B to the brazing material it is possible to add Pas a melting point decreasing element within the scope of the invention.The amount of P is in such a case maximum 15 wt %. If P replaces B assupplement to Si as liquidus temperature lowering element then P maysuitably be within a range from about 0.1 wt % to about 15 wt %.According to another embodiment may P be within a range from about 0.5wt % to about 15 wt %.

According to one embodiment may the brazing material comprise from about8 wt % to about 20 wt % Si. According to another embodiment may theiron-based brazing material comprise from about 7 to about 16 wt % Si.The active, dissolved amount of Si could suitably be within the saidrange in order to obtain the desired lowering of the melting point. Theanalyzed amount of Si might however be considerably higher, since Si mayoccur in the state of silicon carbides or silicon borides, silicon couldbe bonded to oxygen or be chemically bonded in some other way. Accordingto yet another embodiment may Si be within the range from about 8 toabout 12 wt %.

The iron based brazing material may contain one or more micro alloyingelements such as V, Ti, W, Al, Nb, Ta and others. The content ofmicro-alloying elements in the brazing material may be within the rangeof from about 0 wt % to about 1.5 wt %. The contents of micro-alloyingelements may be within the range of from about 0 wt % to about 1.5 wt %for each micro-alloying element present in the brazing material.Variations in composition may also be a consequence of small inevitableamounts of contaminating elements as C, O and S.

The brazing material according to one embodiment comprises an iron-basedbrazing alloy which alloy comprises from about 9 wt % to about 30 wt %Cr, from about 5 wt % to about 25 wt % Ni, from about 0 wt % to about 9wt % Mo, from about 0 wt % to about 5 wt % Mn, from about 0 wt % toabout 1 wt % N, from about 8 wt % to about 20 wt % Si, from about 0.1 wt% to about 1.5 wt % B. The brazing alloy may comprises contaminatingelements as at least one of C, O, and S. Optionally the brazing alloymay also comprise at least one micro-alloying element as V, Ti, W, Nb,or Ta, and the micro-alloying element may be less than 1.5 wt % in thebrazing alloy.

According to another embodiment may the iron based brazing materialcomprise from about 8 to about 16 wt % Si. According to yet anotherembodiment may Si be from about 10 wt % to about 16 wt % Si. Accordingto a further embodiment may be from about 8 to about 12 wt %. Accordingto a further embodiment may be from about 10 to about 12 wt %.

The iron-based brazing alloy may comprise Mo within the range of fromabout 0.5 wt % to about 7 wt % Mo according to one embodiment. Accordingto another embodiment may the brazing material comprise Mo within therange of from about 1 wt % to about 3.5 wt % Mo.

The brazing alloy may also comprise Mn within the range of from about0.1 wt % to about 5 wt % Mn. According to another embodiment may thebrazing alloy comprise Mn within the range of from about 0.1 wt % toabout 3 wt % Mn.

According to yet another embodiment may the iron-based brazing alloycomprise from about 14 wt % to about 25 wt % Cr, from about 6 wt % toabout 24 wt % Ni, from about 0.5 wt % to about 7 wt % Mo, from about 0wt % to about 5 wt % Mn, from about 0 wt % to about 1 wt % N, from about8 wt % to about 14 wt % Si, from about 0.2 wt % to about 1.5 wt % B, andinevitable amount of contaminating elements as at least one of C, O, andS. Optionally may the brazing alloy also comprise at least onemicro-alloying element as V, Ti, W, Nb, or Ta, and the micro-alloyingelement is less than 1.5 wt % in the brazing alloy. According to anotherembodiment may the amount of Mn be within the range of from about 0.1 wt% to about 5 wt % Mn. In another embodiment may the amount of Si is fromabout 10 wt % to about 12 wt % Si. In yet another embodiment may theamount of B be from about 0.4 wt % to about 1.0 wt % B.

The iron based brazing material according to the invention may withadvantage produced by gas atomization or water atomization. If the alloycontains boron it is also possible to produce the brazing material bymelt spinning. Another possible method to produce the brazing materialmay be produce ingots which will be cursed and grounded to desiredparticle size.

The invention also comprises a brazed product produced by brazingtogether iron based objects, by which the product is characterized bythe joining of the objects with a iron based brazing material which isan alloy with the composition mentioned above.

The brazed product is with advantage a plate heat exchanger intended forat least two heat exchanging media, which comprises at least one platepackage manufactured by brazing together a number of thin walled heatexchanger plates of an iron-based material by means of an iron-basedbrazing material. The heat exchanger plates define between themselvesplate inter spaces intended for the heat exchanging media. The brazingjoints have a metallurgical composition close to the composition of theiron based plate material with locally higher amounts of Si in andaround the brazing joints in comparison with the iron based platematerial.

When the expression thin walled is used in connection with plate heatexchangers it is used for plates with a thickness below 1 mm. Such thinplates are necessary in order to obtain an efficient heat transfer.

The brazed product may with advantage be brazed with an iron basedbrazing material containing Si together with B or P.

For thin walled products as plate heat exchangers it is important tohave the right relation between the amount of boron in the brazingmaterial and the weight of the plates to be brazed. In such a case thepercentage of boron will be maximum 1.5 wt % in order to avoid excessiveformation of chromium borides as will be described below.

For brazing of iron based materials one has as traditionally used Cu- orNi-brazing materials as mentioned earlier. Surprisingly it has now beenfound that one may start with a base material with the same compositionas the material in the objects one desires to join together. By alloyingsuch a material with silicon one may obtain well functioning brazingmaterials. By studying binary phase diagrams for pure iron and Si, B andP one may find that a Fe—Si alloy has a melting point minimum of 1212°C. at around 19 wt % Si. For a Fe—B alloy there is a melting pointminimum at about 1174° C. for about 4 wt % B. In the Fe—P system thereis a melting minimum at about 1048° C. at about 10 wt % P.

In most cases pure iron materials are not used but instead alloys areused, which apart from Fe also contains relatively large amounts of Crand Ni. In many alloys there are also Mo, Mn, Cu and N.

In order to obtain a brazing joint the liquidus temperature of thebrazing material ought to be below 1220° C.

Surprisingly enough it has been found that an addition of a relativelyminor amount of silicon may give such a lowering of the liquidustemperature that a suitable brazing material may be obtained.

According to the present invention it is stated that the percentage ofboron should be below 1.5 wt %. The reason for this is that the boron iscontrast to the silicon diffuses very rapidly into and in the iron basedmaterial being brazed. This affects the performance of the brazedproduct. The best braze joints are obtained if the gap between theelements to be joined is as small as possible. The applied braze fillercreates a distance between the elements to be joined due to thethickness of the braze filler in the gap. When brazing, the braze fillermelts and will be pressed aside, allowing the gap to decrease. In manycases, when brazing objects, as for example plate heat exchangers, theperimeter of the objects will be heated more rapidly than the interiorof the object. Consequently also the brazing material starts to melt atthe perimeter. Boron starts to diffuse and with that the brazingmaterial starts to solidify, due to the change in the composition, atthe perimeter before the brazing material in the interior has melted.According to the proposed invention silicon is the element used fordecreasing the melting point and boron only to a smaller extent as amelting point decreasing element. Since silicon diffuses slower thanboron the diffusion time increases so that the braze filler in theinterior parts can melt before the outer parts solidify. The function ofboron is mainly to increase the wettability of the brazing material.

An additional reason for avoiding a high content of boron is when thebrazing alloys containing chromium. Many stainless steel contain around17 wt % Cr. The chromium content governs to a great extent the corrosionproperties of the stainless steel. If there is chromium in the object tobe brazed and boron in the brazing material there is a risk forformation of chromium borides. Each boron atom binds 3.8 chromium atomsif the formula for the boride is Cr 23B6. Also the fact that therelationship in the molecule weight between Cr and B is 52.0/10.8=4.8shows that even small percentages, e.g. 2-3 wt % B may decrease thechromium content to such an extent that it will have severe effects onthe corrosion resistance. The corrosion resistance of the steel willdecrease with each boride that is formed. The chromium borides will beharder than the base material and have also a needle formed shape. Theirshape may give rise to stress concentration and consequently crackformation.

The present invention is of great value for brazing different kinds ofobjects of steel. As an example the stainless steel, alloy 316, may bementioned. The chemical composition of this alloy is max. 2.0 wt % Mn,16.5-18 wt % Cr, 10.0-13.0 wt % Ni, 2.0-2.5 wt % Mo, the balance beingFe. According to the invention, a brazing material is prepared with thesame composition as the alloy but with a suitable amount of Si replacingthe same amount of Fe by weight, and Si is supplemented by B or P in thebrazing material. After the brazing process the brazed product will havemainly the same composition in the brazed objects as in the brazingjoints.

Another example of a suitable chemical composition for brazing thestainless steel alloy 316 could be the brazing alloy having from about16 to about 18.5 wt % Cr, from about 10 to 14 wt % Ni, from about 1.8 toabout 2.2 wt % Mo, from about 1 to about 2 wt % Mn, from about 10.5 toabout 11.5 wt % Si, from about 0.5 to about 0.6 wt % B, and the balancebeing Fe. After the brazing process the brazed product will have mainlythe same composition in the brazed objects as in the brazing joints.

The brazing material according to the invention is suitably made in theform of a powder. The powder may be manufactured by producing an ingot,which thereafter is crushed and milled. The brittle nature of thematerial is utilized by this manufacturing method. The disadvantageswith ingot casting are that a certain risk for segregation may give riseto a non homogenous material with a melting interval which is difficultto define or is broad. For smaller ingots and/or a rapid cooling therisk for segregations is reduced. In ingot casting it is important tominimize the contact with air by using vacuum casting or casting with ashielding gas. As a consequence of the mechanical treatment the energycontents of the brazing material increases and with that its reactivity.

Further manufacturing methods to produce a powder with a homogenouscomposition consist of water atomization or gas atomizing. Theproperties of the powder vary with the manufacturing method. The crushedand milled particles are angular and pointed, the water atomizedparticles are nodular and the gas atomized particles are almostspherical. This difference in particle shape gives the brazing materialsomewhat varying properties when used for brazing. By choosing differentatomizing methods and crushing/milling extent combined with screeningthe distribution of the particles size may be controlled. In wateratomizing the oxygen content generally will be higher since wateratomizing takes place at a higher oxygen potential than gas atomizing. Ahigher oxygen content may gives rise to formation of Si-oxides in thematerial which may have a negative influence on the mechanicalproperties of the brazing joint. The effective Si-percentage in thebrazing material will consequently be lower, which means that themelting interval will be displaced.

The brazing material according to the invention may be applied on theplaces where one desires a brazing joint by means of different methods.A powder of the brazing material manufactured by any of the describedmethods may be suspended in some binder in order to be applied in somesuitable manner.

Example 1

In example 1 different alloy compositions were tested and the brazingmaterials were produced by melting in a small vacuum furnace. The ingotswere thereafter allowed to solidify in the moulds. In Table 1 there areshown different examples of compositions of brazing materials.

TABLE 1 Analysis of some experiment melts Alloy Fe % Si % Mn % P % B %Cr % Mo % Ni 1 Bal 6 1 0 0 17 2.5 12 2 Bal 8 1 0 0 17 2.5 12 3 Bal 10 10 0 17 2.5 12 4 Bal 12 1 0 0 17 2.5 12 5 Bal 15 1 0 0 17 2.5 12 6 Bal 61 0 1.5 17 2.5 12 7 Bal 6 1 3 0 17 2.5 12 8 Bal 10 1.5 17 2.5 20The expression Bal (balance) means that the remaining material in themelt consists of Fe. The actual composition of the melts after the castwas measured and summarized in Table 2.

TABLE 2 Measured percentage in the ingot. Al- ppm loy Fe % Si % Mn % P %B % Cr % Mo % Ni O• 1 Bal 5.86 1.43 17.1 2.45 11.9 2 Bal 8.20 1.29 17.22.51 11.9 3 Bal 10.0 1.25 17.1 2.46 12.0 (56: 57) 4 Bal 12.1 1.20 16.82.47 11.9 (31: 31) 5 Bal 14.7 1.81 16.6 2.54 11.9 (38: 42) 6 Bal 5.931.46 1.20 16.7 2.42 11.9 7 Bal 6.37 1.60 3.09 17.2 2.51 11.6 8 Bal 10.01.47 16.4 2.54 20.5 (27: 30) •Two measurementsA powder was produced from the experimental melts according to Table 2,and brazing tests were carried out in a vacuum furnace. The maximumtemperature in the furnace was about 1190° C. The specimens wereexamined visually for a determination, if the alloy had melted or not,if the alloy had reached and passed the solidus temperature or hadmelted completely, and thus had reached the liquidus temperature. Theresults are summarized in Table 3. In Table 3 solidus- and liquidusproperties were visual determined after the test brazing at 1190° C. ina vacuum furnace.

TABLE 3 Visual determination of the solidus- and liquidus propertiesafter test brazing at 1190. degree. C. in a vacuum furnace.Melt >Solidus >Liquidus 1 Yes No 2 Yes Close 3 Yes Yes or close 4 YesYes 5 Yes Yes 6 Yes No 7 Yes No 8 Yes CloseAs may be seen in Table 3 melts 2 to 5 and 8 indicate, that the materialmay be suitable for brazing material at a brazing temperature below1200° C.

FIGS. 1 to 3 show how the melts 2, 3 and 5 have been examined formeasurement of the melting interval in a DTA-equipment (DifferentialThermal Analysis). The measurement is performed by heating the materialin two stages from room temperature to a temperature of 900° C. andthereafter to a maximal temperature of 1300° C. The material isthereafter cooled to a temperature of 900° C. The heating and thecooling are repeated twice. The peaks, which overlap each other andpoint downward in the diagram, show the amount of heat needed to achievemelting. The extension of the peak constitutes a measure of the meltinginterval of the studied alloy.

FIG. 1 shows the DTA curve for melt no. 2, FIG. 2 shows the same curvefor melt no. 3 and FIG. 3 for melt no. 5. As may be seen in the figuresthe melting interval for an alloy with about 9% Si is 1154-1197° C.(FIG. 1), for an alloy with 10% Si 1145-1182° C. (FIG. 2) and for analloy with 15% Si 1142-1177° C. (FIG. 3).

The accuracy of the melting interval, or deviations from the value thathas been measured does not only depend on differences in the meancomposition. Apart from the microstructure of the material, the contentof contaminants is also important. Usually contaminating elements are C,O, S and N. At higher O-percentage Si is chemically bonded during theproduction process, which means that the effective, dissolved percentageof Si is reduced. This means that the liquidus temperature and thesolidus temperature increase.

The percentage of carbon influences the melting temperature in such away that a higher C-content usually yields a lower melting interval(lower solidus- and liquidus temperatures), but the corrosion propertiesfor example are influenced in a negative way when brazing an iron basedmaterial as for example alloy 316. Variations of the solidus- andliquidus temperatures with ±10° C. are not unusual.

The accuracy of the value is also depending on which measuringinstrument and on which method that is used for the analysis. Anuncertainty with ±20° C. for the liquidus- and solidus temperatures isnormal for alloys where an analysis with the DTA-method is common.

Further alloy compositions were tested, samples 9 to 14, and the brazingmaterials were produced by melting in a small vacuum furnace. Alloys 9to 12 were brazed at a temperature of 1190° C. and alloys 13 to 14 werebrazed at 1215° C. The ingots were thereafter allowed to solidify in themoulds. The results are summarized in Table 4.

TABLE 4 Al- % % % % % % % % % >Soli- >Liqui- loy Fe Si Mn P B N Cr Mo Nidus dus 9 bal 12.2 1.5 18 0.3 8 Yes Yes 10 bal 18.1 1.2 0 0 0 Yes Yes 11bal 8 1.5 0.5 17 2.2 11 Yes Yes 12 bal 5 1.5 5 17 2.2 11 Yes Yes 13 bal7.8 0.45 0.2 20 6.1 18 Yes Yes 14 bal 13 0.7 13 0 0 Yes Yes

Example 2

To investigate the effect of boron content in iron-based braze filler onbrazed joints etc different amounts of B supplementing Si in theiron-based braze fillers were tested. The amount of elements was app.17.5 wt % Cr, app. 1.4 wt % Mn, app. 13.6 wt % Ni, app. 1.9 wt % Mo,app. 10.0 wt % Si and the boron content varied from 0 wt % to 3.7 wt %all balanced with Fe.

The tests which were used for evaluating the effect of boron content inthe braze fillers on brazed product were wetting tests and corrosiontests. In both test proceedings circular test pieces were used and thepreparations of the test pieces followed the proceedings of the WettingTest Procedure described below.

Wetting Test Procedure

The circular test pieces were made of Stainless Steel, type 316, thetest pieces were 0.8 mm thick and had a diameter of 85 mm. The testpieces were cleaned with detergent and rinsed with de-ionised water andacetone, 2.0 g of brazing filler was applied in the centre of eachcircular test piece. All the circular test pieces were then brazed withthe same type of brazing cycle. The circular test pieces were brazed ata temperature of about 1200° C. for 1 hour.

Wetting and Flow Ability Test with the Circular Test Pieces.

The wetting and flow ability test were carried out by measuring thebrazed area after each brazing cycle. The results from the wetting andflow ability tests were summarized in Table 5 where the wetted area ofthe braze filler is measured in mm². The results are also presented inDiagram 1, see FIG. 4.

TABLE 5 Wetting tests Wetted Area Wetted Area Wetted Area Wetted Area BBraze Cycle 1 Braze Cycle 2 Braze Cycle 3 Braze Cycle 4 [wt %] [mm²][mm²] [mm²] [mm²] 0  64* 0  95* 0  154* 0.26 415 0.26 491 0.43 0.43 5310.6 346 0.6 254 0.6 346 0.6 283 0.6 314 0.6 346 0.6 491 0.6 572 0.6 5721.2 415 1.2 452 1.3 491 1.8 531 2.5 572 2.6 415 3.6 283 3.6 201 3.7 572*For all test samples with 0 wt % B, wetting angles larger than 90° werefound. The rest of the test samples did not show any wetting angleslarger than 90°. The wetting angles were evaluated by ocular inspectionin a light optical microscope (LOM).

The wetting tests clearly show that if no boron is added to the brazingfillers, then the wetting angle is larger than 90° which were found forall tested samples with 0 wt % B. A wetting angle larger than 90° meansthat there is no wetting. The wetting test also shows that the wettedareas of the samples with no added boron are smaller than the wettedareas of those samples having added boron and that by adding smallamounts of B the wetting area increases rapidly.

Corrosion Tests

Corrosion tests were carried out using the same type of the circulartest pieces which was used in the wetting tests. 2.0 g of brazing fillerwas applied in the centre of each circular test piece. The circular testpieces were brazed at a temperature of about 1200° C. for 1 hour. Thecorrosion rates were determined by weight loss measurements. The pieceswere sectioned before the corrosion testing to adapt the width of thetest pieces to the test rig, and the test pieces were corrosion testedin 16 vol-% Sulphuric acid (ISO 3651-2 Method A). The results arepresented in Table 6 and in Diagram 2, see FIG. 5.

TABLE 6 Corrosion tests Braze Start Stop Difference Weight Filler Bweight weight Area Time in weight loss [wt %] [gram] [gram] [cm²] [days][grams] [%] 0.60 10.672 10.646 31 1 0.026 0.239 1.30 9.797 9.773 29 10.024 0.245 1.50 10.710 10.682 30 1 0.028 0.261 1.80 10.755 10.717 31 10.038 0.355 2.60 10.700 10.641 32 1 0.059 0.551 3.70 10.673 10.625 32 10.047 0.440

The corrosion results clearly show that for iron-based fillers havinglow contents of boron the weight losses are much lower than foriron-based fillers having high contents of boron. At boron contentswhich are higher than about 1.5 wt % the corrosion properties stronglydecreases. Diagram 2 shows the weight losses in relation to content ofboron in the iron-based brazing fillers.

Example 3

Four different iron-based braze filler alloys according to the inventionwere produced to investigate the relationship between silicon and boronon the melting of the iron-based braze fillers. Two of the brazefiller's melting point interval were tested, i.e. sample 1 and sample 2.Both fillers melted below 1200° C. The results are presented in Table 7.All of the iron-based braze fillers were braze tested in a vacuumfurnace at app 1200° C. After brazing the braze results was ocularinspected, i.e. sample 3 and sample 4 but of course also the first twosamples. All of the fillers (samples 1 to 4) were completely melted andwere thus possible to use as braze fillers.

TABLE 7 Relationship of Si and B within the brazing alloy in connectionto melting properties. Melting Fe Cr Mn Ni Mo Si B Interval Sam- [wt [wt[wt [wt [wt [wt [wt or Melted ple %] %] %] %] %] %] %] below [° C.] 1 5716.8 1.48 11.8 2.15 10.27 0.49 1111-1140 2 55 17.1 1.57 11.8 2.17 11.740.49 1113-1149 3 55 17.1 1.38 14.58 1.85 9.5 0.63 1200 4 57 17.2 1.4113.2 2.01 8.5 0.9 1200

Example 4

Four different iron-based braze filler alloys according to the inventionwere produced to investigate the relationship between silicon andphosphorous on the melting of the iron-based braze fillers. All of theiron-based braze fillers were braze tested in a vacuum furnace at app1200° C. After brazing the braze results was ocular inspected. All ofthe fillers (samples 5 to 8) were completely melted and were thuspossible to use as braze fillers. The results are presented in Table 8.

TABLE 8 Relationship between Si and P within the brazing alloy inconnection to melting properties. Fe Cr Mn Ni Mo Si P Melted Sam- [wt[wt [wt [wt [wt [wt [wt below ple %] %] %] %] %] %] %] [° C.] 5 58 16.201.43 11.60 2.19 7.66 3.10 1200 6 56 16.90 1.55 12.21 2.00 8.80 2.60 12007 53 17.40 1.60 11.02 2.21 6.19 8.10 1200 8 55 16.89 1.44 11.50 2.2011.90 0.90 1200

1. An iron-based brazing material comprising a brazing alloy, whichalloy comprises: from about 9 wt % to about 30 wt % Cr; from about 5 wt% to about 25 wt % Ni; from about 0 wt % to about 9 wt % Mo; from about0 wt % to about 5 wt % Mn; from about 0 wt % to about 1 wt % N; fromabout 6 wt % to about 20 wt % Si; wherein at least one of the B and theP are present as a melting point lowering supplement to Si, and whereinB is from about 0.1 wt % to about 1.5 wt %, or wherein P is from about0.1 to about 15 wt % P; and contaminating elements as at least one of C,O, and S; and optionally the brazing alloy also comprises at least onemicro-alloying element as V, Ti, W, Nb, or Ta, and the micro-alloyingelement is less than 1.5 wt % in the brazing alloy; wherein all valuesare stated in weight percent, wherein the Si, B and P lowers theliquidus temperature, that is the temperature when the brazing materialis completely melted.
 2. The brazing material according to claim 1,wherein the amount of P is within the range of from about 0.5 wt % toabout 15 wt % P.
 3. The brazing material according to claim 1, whereinthe amount of B is within the range of from about 0.2 wt % to about 1.5wt % B.
 4. The brazing material according to claim 1, wherein the amountof Si is within the range of from about 8 wt % to about 20 wt % Si. 5.The brazing material according to claim 1, wherein the alloy is balancedwith Fe.
 6. An iron-based brazing alloy comprising: from about 9 wt % toabout 30 wt % Cr; from about 5 wt % to about 25 wt % Ni; from about 0 wt% to about 9 wt % Mo; from about 0 wt % to about 5 wt % Mn; from about 0wt % to about 1 wt % N; from about 8 wt % to about 20 wt % Si; whereinthe brazing alloy also comprises from about 0.1 wt % to about 1.5 wt %;and contaminating elements as at least one of C, O, and S; andoptionally the brazing alloy also comprises at least one micro-alloyingelement as V, Ti, W, Nb, or Ta, and the micro-alloying element is lessthan 1.5 wt % in the brazing alloy; wherein all values are stated inweight percent, wherein the Si and B lowers the liquidus temperature,that is the temperature when the brazing material is completely melted,and B increases the wettability of the brazing alloy.
 7. The brazingalloy according to claim 6, wherein the amount of Mo is within the rangeof from about 0.5 wt % to about 7 wt % Mo.
 8. The brazing alloyaccording to claim 6, wherein the amount of Mo is within the range offrom about 1 wt % to about 3.5 wt % Mo.
 9. The brazing alloy accordingto claim 6, wherein the amount of Mn is within the range of from about0.1 wt % to about 5 wt % Mn.
 10. The brazing alloy according to claim 6,wherein the amount of Mn is within the range of from about 0.1 wt % toabout 3 wt % Mn.
 11. The brazing alloy according to claim 6, wherein theamount of Si is from about 10 wt % to about 16 wt % Si.
 12. The brazingalloy according to claim 6, wherein the amount of Si is from about 10 wt% to about 12 wt % Si.
 13. The brazing alloy according to claim 6,wherein the brazing alloy is produced by gas atomization, wateratomizing, melt spinning, or by crushing, milling, or both of an ingot.14. An iron-based brazing alloy comprising: from about 14 wt % to about25 wt % Cr; from about 6 wt % to about 24 wt % Ni; from about 0.5 wt %to about 7 wt % Mo; from about 0 wt % to about 5 wt % Mn; from about 0wt % to about 1 wt % N; from about 8 wt % to about 14 wt % Si; whereinthe brazing alloy also comprises from about 0.2 wt % to about 1.5 wt %B; and contaminating elements as at least one of C, O, and S; andoptionally the brazing alloy also comprises at least one micro-alloyingelement as V, Ti, W, Nb, or Ta, and the micro-alloying element is lessthan 1.5 wt % in the brazing alloy; wherein all values are stated inweight percent, wherein the Si and B lowers the liquidus temperature,that is the temperature when the brazing material is completely melted,and B increases the wettability of the brazing alloy.
 15. The brazingalloy according to claim 14, wherein the amount of Mn is within therange of from about 0.1 wt % to about 5 wt % Mn.
 16. The brazing alloyaccording to claim 14, wherein the amount of Si is from about 10 wt % toabout 12 wt % Si.
 17. The brazing alloy according to claim 14, whereinthe amount of B is from about 0.4 wt % to about 1.0 wt % B.
 18. Thebrazing alloy according to claim 14, wherein the brazing alloy isproduced by gas atomization, water atomizing, melt spinning, or bycrushing, milling, or both of an ingot.
 19. An iron-based brazing alloycomprising: from about 16 wt % to about 20 wt % Cr; from about 8 wt % toabout 14 wt % Ni; from about 1.5 wt % to about 3.5 wt % Mo; from about 0wt % to about 2 wt % Mn; from about 0 to about 1 wt % N from about 10 wt% to about 12 wt % Si, wherein the brazing alloy also comprises fromabout 0.4 wt % to about 0.8 wt % B; and contaminating elements as atleast one of C, O, and S, and optionally the brazing alloy alsocomprises at least one micro-alloying element as V, Ti, W, Nb, or Ta,and the micro-alloying element is less than 1.5 wt % in the brazingalloy; wherein all values are stated in weight percent, wherein the Siand B lowers the liquidus temperature, that is the temperature when thebrazing material is completely melted, and B increases the wettabilityof the brazing alloy.
 20. The brazing alloy according to claim 19,wherein the brazing alloy is produced by gas atomization, wateratomizing, melt spinning, or by crushing, milling, or both of an ingot.21. A brazed product manufactured by brazing objects with an iron basedalloy according to claim 1, wherein the material in the objects to bebrazed is iron-based.
 22. The brazed product according to claim 21,wherein the product is a plate heat exchanger intended for at least twoheat exchanging media, which comprises at least one plate packagemanufactured by brazing together a number of thin walled heat exchangerplates of an iron based material brazed by means of an iron basedbrazing material, at which the heat exchanger plates between themselvesdefine plate inter spaces intended for the heat exchanging media, atwhich the brazing joints have a metallurgical composition close to thecomposition of the iron based plate material with locally higher amountsof Si in and around the brazing joints in comparison with the iron basedplate material.